Television (TV) networks have traditionally utilized analog signal formats to carry video and audio channels to television viewers or subscribers. All the television signals may each be modulated at a different radio frequency (RF) and combined or multiplexed for transmission over the terrestrial air or a hybrid fiber-coaxial cable network. The customer premise equipment (CPE), such as a TV set or cable set-top box converter, receives all such signals combined, and tunes to a particular frequency in order to display the TV channel desired by the viewer.
With various advancements in digital communications and the introduction of digital television (DTV), TV network providers have been replacing or otherwise upgrading their transmission and distribution systems to provide new and/or better quality services to their viewers or paid subscribers. In addition to transmitting analog signals, the infrastructure of these upgraded or new systems are also adapted to facilitate the generation and transmission of various digital formats that provide superior picture and sound quality, higher channel capacity, high-speed Internet data services, voice services and/or interactive services. Given the size of existing television infrastructure, television network providers must also provide support for legacy systems, and therefore, provide support for both analog and digital television systems.
Since a plurality of analog and/or digital channels are multiplexed onto and transmitted by the TV network provider infrastructure, the CPE must have the capability to detect or discriminate whether a signal is in analog format or digital format. Once an incoming signal for a channel is determined to be either in digital or analog format, the proper demodulation or decoding scheme is utilized to process the channel.
Current analog TV signals are defined primarily by the National Television Standards Committee (NTSC), the Phase Alternative Line (PAL) or the Sequential Couleur Avec Memoire (SECAM) systems, and used in different countries around the world. An analog TV signal utilizes mainly two RF carriers, combined in the same channel band. One carrier may commonly be amplitude modulated (AM) with video content, and the other may be frequency modulated (FM) with audio. In operation, an analog TV receiver must adjust the signal power, separate the video and audio carriers, and lock to each carrier in order to down-convert the signals to baseband. The baseband video signal may then be decoded and displayed by achieving horizontal and vertical synchronization and extracting the luminance and color information. After demodulating the received signal, the resulting baseband audio may be decoded, and left, right, surround channels and/or other information may be extracted.
Current digital TV signals utilizes a plurality of modulation techniques for transmitting and receiving packetized information comprising one or more digitized and compressed TV programs, Internet data and/or voice data. A digital TV signal utilizes primarily one RF carrier that is modulated with either quadrature amplitude modulation (QAM) of different levels including quaternary phase shift keying (QPSK), or vestigial sideband (VSB) modulation, among other schemes. A digital TV receiver must adjust the signal power, lock to the carrier, and down-convert it to baseband. The baseband digital signal is demodulated choosing QAM or VSB schemes by trying both, error corrected, and synchronized as a valid bit stream. The bit stream is further decompressed to reproduce the picture and sound, or processed as Internet data or voice data.
In a conventional TV CPE, after tuning to a channel frequency, the TV set or set-top box normally detects whether a channel contains an analog or digital signal, or any signal at all, by performing many of the receiving functions outlined above. If the receiver successfully creates and validates a bit stream from the RF carrier, then it found a digital QAM or VSB signal. If a receiver successfully locks to the video and audio carriers, then it found an analog TV signal. Otherwise it found no signal at all. This process is relatively long and causes delays when scanning TV channels.
In a cable modem used for receiving Internet data, the cable modem receiver must detect only digital QAM signals. When a cable modem has to wait until a valid bit stream is created for each detection attempt, the usual latency associated with a connection increases. Furthermore, the latency due to the waiting process is further exacerbated when the modem has to scan all the available RF channels in order to determine which RF channel contains the appropriate Internet information.
Further limitations and disadvantages of conventional and traditional approaches will become apparent to one of skill in the art, through comparison of such systems with some aspects of the present invention as set forth in the remainder of the present application with reference to the drawings.